Providing a cost effective, robust communications infrastructure using wireless local area networking (WLAN) technologies is a challenge in enterprise office environments. For example, the area to be covered within the office environment is diverse in size and shape (e.g. corridors, stairwells, atriums, conference rooms, workstation cubicles, etc.). The transmission path between a WLAN-enabled client device and a WLAN access point may be obscured by the building infrastructure (e.g. walls, support columns, stairways), by office equipment (e.g. book cases, storage units, cubicle partitions, etc.), and by the office workers themselves. In addition, the transmission path may be affected by other equipment operating in the area (e.g. microwave ovens, cellular phones, other WLAN devices, etc.) producing interference that disrupts communications.
Some elements of the environment are fairly static (e.g. the supporting walls and columns of the building structure) and can be dealt with to some degree during initial planning and deployment of the WLAN system. Office equipment, decorations, banners and other furnishings come and go over the lifetime of the WLAN installation and can have an effect on WLAN operation that cannot be anticipated during the planning stages. Interference, whether intentional or unintentional, cannot be anticipated and must be dealt with as it occurs.
Unanticipated changes in the environment may be dealt with either by modifying the operating parameters of a transmission (e.g. the modulation scheme, the channel frequency), by adjusting the coverage pattern (e.g. through beamforming), or by finding an alternate path between the transmitter and receiver.
Traditionally, finding an alternate path in a WLAN environment means that the client device must look for another access point within range of its transmission. Normal operation of applications running on the client device may be disrupted during the time that it takes for the client device to find a new access point and to establish a connection through that access point.
MIMO technology—recently introduced into the 802.11 WLAN and into a number of cellular communications standards—provides another means for establishing multiple paths between an access point and a client device.